Study On Microstructure And Mechanical Properties Of Mg-Gd-Dy-Zn-Zr Cast Magnesium Alloy

The existing high strength magnesium alloy strength and plasticity can not meet the actual needs,so it is the general trend and the expectation of the public to further study the magnesium alloy with higher strength and plasticity.In recent years,Mg-Gd-based magnesium alloys have been highly anticipated due to their very high strength,and the research and development of Mg-Gd-based magnesium alloys are in full swing.At present,the most researches on Mg-Gd-based alloy are on Mg-Gd-Y base,but the problem of low elongation exists in Mg-Gd-Y base alloy.However,the crystal structure,atomic radius and physical and chemical properties of Y and Dy are similar,and Dy has higher solid solution degree and more obvious solid solution strengthening effect than Y.Therefore,the Mg-XGd-4Dy-2Zn-0.5Zr and Mg-8Gd-XDy-2Zn-0.5Zr Mg-Gd-based high strength cast magnesium alloys have been designed and developed in this paper.On this basis,the microstructure and mechanical properties of Mg-xGd-4Dy-2Zn-0.5Zr and Mg-8Gd-x Dy-2Zn-0.5Zr test magnesium alloys were studied,which are of great significance and value.Based on the existing research results of Mg-Gd-RE based cast magnesium alloys,the Mg-xGd-4Dy-2Zn-0.5Zr and Mg-8Gd-x Dy-2Zn-0.5Zr cast magnesium alloys with changes in Gd content were designed and prepared.On this basis,the microstructure of Mg-xGd-4Dy-2Zn-0.5Zr and Mg-8Gd-x Dy-2Zn-0.5Zr test magnesium alloys in different states were studied and compared by OM,XRD,SEM and EDS,and the mechanical properties and hardness of the alloys were measured at room temperature.The following results were obtained:(1)The as-cast Mg-xGd-4Dy-2Zn-0.5Zr alloy is mainly composed of?-Mg,skeletal Mg₃(Gd,Dy,Zn)eutectic phase and stripy long-period Mg₁₀(Gd,Dy,Zn)phase.After solution treatment,the skeletal and striped phases were dissolved,and massive Mg₁₂(Gd,Dy,Zn)phases and fine lamellar phases(LPSO structural phase)were precipitated.After aging at 225?for 24h,the grain boundary is clearly visible,the residual gray phase continues to dissolve,and the dispersion strengthening phase precipitates.The microstructure changes of Mg-8Gd-xDy-2Zn-0.5Zr alloy are basically the same as those of alloys with different Gd contents.(2)In the heat treatment of Mg-8Gd-4Dy-2Zn-0.5Zr alloy,the most important factor of tensile strength is the solution time.The most important factor for yield strength is solution temperature.The most important factor affecting the elongation is aging temperature.(3)In the selected range of Gd composition,the strength and elongation of Mg-xGd-4Dy-2Zn-0.5Zr alloy are the highest and lowest when the content of Gd is12wt.%.The tensile strength,yield strength and elongation in the aging state are 342MPa,211MP and 3.0%,respectively.(4)When the content of Dy is 4wt.%in Mg-8Gd-x Dy-2Zn-0.5Zr alloy,the comprehensive properties of the alloy are better in the range of selected Dy composition.The tensile strength,yield strength and elongation in solid solution state are269MPa,132MP and 18.0%,respectively.The mechanical properties of the aged alloy are lower than those of the solid solution alloy.